A copyright protection scheme for digital images using visual cryptography technique Der-Chyuan Lou, Hao-Kuan Tso and Jiang-Lung Liu The Computer Standards & Interfaces Volume: 29, 2006 指導老師：李南逸 Speaker ：黃資真

Outline Introduction Visual cryptography Secret image generation Watermark extraction Conclusions

Introduction Visual cryptography technique Extract the feature from the protected image Generate a secret image

Visual cryptography

Secret image generation (1/3) IA protected image W’’A watermark KA secret key CA codebook LLow sub-band MMiddle sub-band nNormal-distribution random bit-sequence fFeature value SA secret image

Secret image generation (2/3) Input ： I, W, K, C Output ： S  Step 1 ：  Step 2 ： Extract L and M.  Step 3 ： n = bit-sequence generated by K Three-level DWT I

Secret image generation (3/3)  Step 4 ：  Step 5 ： If f(i,j) = 1 and mod(i+j,4) = 0 If W(i,j) = 0 S(m,n) = [1 0] Else S(m,n) = [0 1] End  Step 6 ： Register to CA for the secret image

Watermark extraction(1/4) I’A suspected image SSecret image KA secret key CCodebook nNormal-distribution random bit-sequence W’’A watermark L’Low sub-band M’Middle sub-band f’Extract the feature value PPublic image

Watermark extraction(2/4) Input ： I’, S, K, C Output ： W’’  Step 1 ：  Step 2 ： Extract L’ and M’  Step 3 ： n = generated by K Three-level DWT I’

Watermark extraction(3/4)  Step 4 ：  Step 5 ： If f ’(i,j) = 1 and mod(i+j,4) = 0 P(m,n) = [1 0] End

Watermark extraction(4/4)  Step 6 ：  Step 7 ：

Conclusions A secret image is generated by utilizing the codebook of visual cryptography. The secret image is registered to CA for further protection. Watermark can be extracted by performing the XOR operation between the secret image and the public image.